US4001555A - Signal processing apparatus - Google Patents

Signal processing apparatus Download PDF

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Publication number
US4001555A
US4001555A US05/610,848 US61084875A US4001555A US 4001555 A US4001555 A US 4001555A US 61084875 A US61084875 A US 61084875A US 4001555 A US4001555 A US 4001555A
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signal
break
point
pulses
sampling period
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Expired - Lifetime
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US05/610,848
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English (en)
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Peter Stanley Levis
Geoffrey Shepherd
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Ferranti International PLC
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Ferranti PLC
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06G—ANALOGUE COMPUTERS
    • G06G7/00—Devices in which the computing operation is performed by varying electric or magnetic quantities
    • G06G7/12—Arrangements for performing computing operations, e.g. operational amplifiers
    • G06G7/26—Arbitrary function generators
    • G06G7/28—Arbitrary function generators for synthesising functions by piecewise approximation

Definitions

  • This invention relates to signal processing apparatus in which an information input signal is weighted in accordance with a mathematical transfer function.
  • a typical analogue apparatus employs a resistive potential divider between input and output terminals, one or more arms of the divider having a plurality of resistors of different values connected in parallel and each of which may be switched into the circuit in turn as the input signal increases.
  • Switching is normally achieved by means of a transistor or diode in series with each resistor and biased in a non-conducting state by a secondary potential divider; as the input variable exceeds the threshold levels required to bias the transistor or diode into conduction additional resistors are added to the potential divider to modify the output.
  • the transfer function is a straight-line section having a slope proportional to the ratio of the potential divider. Because of the interdependency between the resistor values it is not simple to make variations between the threshold levels nor to arrange for other than straight line sections which increase in gradient at each threshold.
  • a digital form of weighting apparatus is described in British patent specification No. 1,351,305 in which the input signal in digital form is compared with one or more stored transfer functions and weighted accordingly. Such device is complex and realisable as a monolithic integrated circuit. In this form it is restricted to the transfer functions provided during manufacture.
  • signal processing apparatus for weighting an input signal in accordance with a predetermined mathematical transfer function represented by a plurality of straight lines each of which intersects the next at a separate break-point
  • apparatus comprises control means operable to define a succession of sampling periods of equal duration, input means responsive to an input signal to provide a train of pulses such that the number of pulses generated during a sampling period represents the magnitude of the input signal, detection means defining the number of pulses corresponding to each successive break-point and responsive to the number of pulses occurring during a sampling period to produce a break-point signal identifying the highest break-point defined by said number of pulses, means responsive to the break-point signal to produce a gradient signal indicative of the slope of the straight line joining the said identified break-point to the next higher break-point, counting means operable to count the number of pulses occurring in excess of the number identifying the break-point, means responsive to the number of pulses counted and to the gradient signal to provide an intermediate signal representative of the product of the input signal, in excess of
  • FIG. 1 illustrates the form of a typical transfer function showing the output signal level as a function of the input signal level
  • FIG. 2 is a block circuit diagram of a signal processing apparatus according to the present invention.
  • FIg. 3 illustrates a further form of transfer function
  • FIG. 4 shows the waveform of a typical output signal of the apparatus of FIG. 2;
  • FIG. 5 shows a further form of transfer function
  • FIg. 6 shows a modified form of part of the block circuit diagram of FIG. 2.
  • the sections have slopes, or gradients S o , S 1 , S 2 , and S 3 respectively and the corresponding values of y at the break points are C o , C 1 , C 2 and C 3 respectively.
  • the value of y can be obtained for any value of x.
  • Section 100 is an input and control section and comprises input means comprising an input terminal 110, an oscillator 120, a gate 130 and control means comprising a control timing element 140.
  • the control timing element 140 defines a succession of sampling periods of equal duration.
  • the oscillator 120 is operable to provide a train of pulses the repetition frequency of which is determined by the amplitude of an analogue input signal x applied to the terminal 110.
  • the gate 130 is connected in line with the oscillator output and is caused to open and close by the timing element 140 to pass pulses only during preset sampling periods. It will be appreciated that by choosing a sampling period of suitable duration the number of pulses produced in the sampling period is directly proportional to the magnitude of x.
  • This section 200 comprises detection means 210 consisting of four pulse-count detectors 211, 212, 213 and 214 to all of which detectors the oscillator pulses are applied.
  • individual detectors are associated with different break-points so that at the end of any sampling period the detector which is producing a detection signal is indicative of the range of values of x (x.sub. i to x i +1 ) within the which the actual value of x lies.
  • the detectors are connected to provide an output to individual sections of a store 220.
  • the store is arranged to be triggered, at the end of each sampling period, by a timing signal from the element 140 to store the detection signal of whichever detector is operating at that time.
  • the output of each section of the store is connected to a digital-to-analogue (D/A) converter 230.
  • the D/A converter comprises a voltage source 231, a resistor network 232 connected to an output line 233, and a plurality of switches forming a switching network 234 by which the voltage source is connected to selected resistors of the network.
  • the voltage applied to the switching network 234 is preset individually for each of the switches to determine the analogue levels of the constants C i .
  • Means for providing a gradient signal shown generally at 240 comprises a plurality of individual voltage sources 241, 242, 243, 244 each connected to receive an output signal from a different detector by way of the store 220.
  • Section 300 determines the ⁇ dynamic ⁇ parameters of the function, that is, the straight-line relationships between break-points.
  • This section includes counting means comprising a pulse counter 310 connected to the gate 130 to receive oscillator pulses serially and operable to produce a parallel binary output, representative of the number of pulses counted, to a store 320 and a counter reset timing means 350 connected to the outputs of the detectors 210 and operable to reset the counter 310 to zero when any of the detector outputs change state.
  • the store 320 is similar to the store 220 and is also triggered at the end of the sampling period by the timing element 140.
  • the store 320 provides an output means for providing an intermediate signal comprising a D/A converter 330 having a resistor network 331 connected to the output line 233 and a plurality of switches 332 to which switches the voltage V i on the line 245 is applied.
  • the voltageV i is representative of the slope S i of the relevant straight-line section and is added together in analogue form a number of times corresponding to the number of stored counter pulses, effectively to multiply the gradient of the slope by the number of pulses, to provide an intermediate signal representative of the portion of the input signal, in excess of the break-point weighted by the slope of the straight-line section.
  • Section 400 comprises output means and an output buffer amplifier 410 to which the output line 233, carrying the analogue break-point and intermediate signals is connected.
  • the amplifier output signal comprising the sum of the analogue outputs is applied to an output terminal 420.
  • the control element 140 also provides a reset signal to the detection means 210 and counter 310 at the end of each period, after the stores 220 and 320 have been triggered.
  • both stores 220 and 320 are empty and provide no output.
  • the frequency of the oscillator is set by the input signal and at the start of the first sampling period the gate 130 is opened and pulses applied to the counter 310 and the detector 210.
  • N o pulses in this case zero
  • the detector 211 provides an output signal to the store 220.
  • N 1 pulses the detector 211 ceases to provide an output and the detector 212 produces an output signal to the store; this change of output signal also resets the counter 310 to zero from where it begins to count for subsequent pulses.
  • N 2 pulses the detector 212 ceases to produces an output signal and the detector 213 produces an output signal to the store; again this change of output signal also resets the counter 310 to zero from where it begins to count for subsequent pulses.
  • N x pulses have been produced comprising (N 2 + number held in counter 310) and the values current at the end of the sampling period are entered into the stores 220 and 320 respectively.
  • the counter 310 and detectors 210 are reset to zero for the next sampling period.
  • the stored values are fed to their respective D/A converters.
  • the store 220 contains information in the form of, say, a binary digit in its third stage corresponding to an output of the detector 213 and this is applied to the D/A converter 230 to provide a break-point signal representative of the constant C 2 .
  • the output of the store 200 also determines which of the voltage sources 240 is to be applied to the A/D converter 330, to which converter the output of the store 320 is applied.
  • the contents of the store 320 comprise the number of pulses (N x - N 2 ) along the straight-line section c and represents the value (X - x 2 ). This number is effectively multiplied by the gradient of the line (representated by the voltage V 2 ) in the D/A converter and the resultant analogue signal comprising the intermediate signal added to that of the constant C.sub. 2.
  • This value y is produced as the output signal for the duration of the next sampling period when, if the value of x has remained unchanged, the same values will be stores and y will be unchanged. If at the end of the next sampling period the value of x has changed then new values will be stored in one or both of the stores and the analogue output will change accordingly for the duration of the next following sampling period.
  • FIG. 3 shows the waveform of a typical output signal varying with time.
  • the output signal (y) be smoothed and/or the sampling period chosen sufficiently short to make any step height between adjacent timing peiods acceptable. It will be appreciated that in any single sampling period the maximum number of pulses produced must not exceed the detection level of the most significant detector (214) or the difference between detection levels exceed the capacity of the counter 310.
  • the frequency of the oscillator is thus required to be chosen sufficiently low not cause overflow of the detectors and counter, but high enough to give sufficient resolution in values of y between successive pulses.
  • the counter and detection means may be provided with additional stages 215 and 311 respectively (shown ghosted) connected to indicator lamps 216 and 312 to show when the stages of either have been overloaded.
  • the detector means 210 may be connected to an output of the counter 310 the output of the counter being supplied to a different detector each time that the count is reset.
  • each detector is concerned only with the number of pulses counted for one particular straight-line section and produces an output signal when the section is complete. Production of such a signal causes the counter 310 to be reset to count pulses for the next straight-line section and causes the counter output for that section to be fed to the next detector. Until the next detector produces an output signal the previously produced output signal is maintained.
  • the detection means 210 may be used in such an arrangement in addition to the counter to provide break-points not havng a factor-of-two relationships.
  • the function of x chosen was represented for four straight-line sections. Any function can be approximated by a suitable number of straight-line sections, requiring an additional detector 210, section of store 200, stage of D/A converter 230 and gradient voltage source 240 for each additional break-point.
  • the straight-line sections all have a positive slope.
  • the circuit arrangement of FIG. 2 may be adapted to handle a negative slope such as that appearing in the transfer function illustrated in FIG. 4.
  • the value of the constant C 3 is arranged to be less than C 2 and the output of the detector 213 is arranged to cause the counter 310 to count down from a preset value in response to the oscillator pulses, output from the next detector 214 returning the counter to zero and causing it to count upwards.
  • the amplifier 410 may be provided with both inverting and non-inverting inputs (not shown).
  • the function generated is that shown by the broken lines in the Figure in that the modulus of each break-point is used and additional break-points employed where the function changes sign.
  • the inputs to the amplifier 410 are gated by the signal on the line 233 becoming zero at the additional break-points to switch the signal between input terminals of the amplifier and provide a negative-going output signal for negative values of the function.
  • the input to the amplifier 410 can be biased by a constant negative signal to displace the transfer function in the y-direction such that a function generated in the wholly positive quadrant is able to produce both positive and negative values of y.
  • the input means comprises an oscillator 150, gating means 160 and a store counter 170.
  • the store counter 170 has a plurality of input terminals 171 by way of which a binary input number, comprising the information input signal, is loaded and stored.
  • the oscillator feeds a continuous train of pulses by way of the gating means 160 to the store-counter which counts down from the stored number.
  • a zero detector in the counter provides an output signal to close the gating means when the stored number of pulses have been passed through.
  • the output of the gating means is applied to the detection means 210 and 310 in place of the output of the gating means 130 shown in FIG. 2. It will be appreciated that for any binary number a train of pulses will be provided having a number of pulses representative of the value of the binary number. If the information input signal is in serial form this may be entered into the store-counter 170 by way of a shift register 180 (shown ghosted in FIG. 6).
  • control timing element 140 is no longer required for the purpose of determining the number of pulses in each sampling period as this number is a function of the input signal and the oscillator frequency.
  • the timing element may therefore be triggered to provide a new sampling period each time that a new value of input signal is presented or may be retained to provide control at fixed duration sampling periods as previously, means then being provided to inhibit operation if the value of the input signal is changing. If the information is contained in other than pure binary form, for example, Gray code or binary coded decimal, then this may be converted to binary before application to the store-counter 170 or shift register 180, as appropriate.
  • the storage means 220 and 320 may be omitted if the switches of the digital-to-analogue converters are caused to latch in on one state by the appropriate detection or counter signals at the end of the sampling period and reset before the application of signals at the end of the next sampling period.
  • the invention as described may be employed to perform mathmatical processes in accordance with a set of different transfer functions or in evaluating the effect of a particular transfer function on a system. Alternatively it may be employed with a fixed transfer function to generate a non-linear relationship between two variables, for example between a vehicle road-speed and vehicle engine throttle-angle, or may be employed to linearise a non-linear relationship, for example output signals of transducers such as thermocouples and pressue transducers.
  • the invention may also be employed in combination with a digital computer, in which an unacceptable amount of store is being utilised to store ⁇ look-up ⁇ tables by which information is weighted; the use of the invention frees the store to enable the machine to perform more complex calculations.
US05/610,848 1974-09-06 1975-09-05 Signal processing apparatus Expired - Lifetime US4001555A (en)

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GB38948/74A GB1501877A (en) 1974-09-06 1974-09-06 Signal processing apparatus
UK38948/74 1974-09-06

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4160272A (en) * 1978-01-05 1979-07-03 Martin Marietta Corporation Digital voltage accumulator
US4190896A (en) * 1978-09-05 1980-02-26 Bell Telephone Laboratories, Incorporated Circuits having substantially parabolic output versus linear input characteristics
US4205386A (en) * 1978-03-01 1980-05-27 The Valeron Corporation Electrocardiographic and blood pressure waveform simulator device
US4318183A (en) * 1978-12-22 1982-03-02 Raytheon Company Multiple channel digital memory system
US4326260A (en) * 1980-07-07 1982-04-20 Norlin Industries, Inc. Linear piecewise waveform generator for an electronic musical instrument
US4393740A (en) * 1979-03-23 1983-07-19 The Wurlitzer Company Programmable tone generator
US4482975A (en) * 1982-03-29 1984-11-13 Motorola, Inc. Function generator
US4667298A (en) * 1983-12-08 1987-05-19 United States Of America As Represented By The Secretary Of The Army Method and apparatus for filtering high data rate signals
US4809203A (en) * 1986-08-25 1989-02-28 Ford Aerospace & Communications Corporation Hybrid analog-digital filter

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58223021A (ja) * 1982-06-21 1983-12-24 Oval Eng Co Ltd 器差調整回路
DE3531118A1 (de) * 1985-08-30 1987-03-12 Micro Epsilon Messtechnik Verfahren zur fehlerkompensation fuer messwertaufnehmer mit nicht linearen kennlinien, sowie anordnung zur durchfuehrung des verfahrens
SE460929B (sv) * 1987-04-24 1989-12-04 Dresser Wayne Ab Saett och anordning foer maetning av volymen av en vaetska som stroemmar genom en maetkammare under en maetperiod
FI101916B (fi) * 1996-12-18 1998-09-15 Nokia Telecommunications Oy Menetelmä muodostaa halutun funktion mukaisesti käyttäytyvä signaalin amplitudi ja muunnin

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Publication number Priority date Publication date Assignee Title
US3345505A (en) * 1960-10-24 1967-10-03 Gen Precision Systems Inc Function generator
US3373273A (en) * 1964-04-17 1968-03-12 Beckman Instruments Inc Analog function generator including means for multivariable interpolation
US3412240A (en) * 1963-02-21 1968-11-19 Gen Precision Systems Inc Linear interpolater
US3480767A (en) * 1967-06-12 1969-11-25 Applied Dynamics Inc Digitally settable electronic function generator using two-sided interpolation functions
US3678258A (en) * 1970-09-29 1972-07-18 Electronic Associates Digitally controlled electronic function generator utilizing a breakpoint interpolation technique
US3729625A (en) * 1970-06-05 1973-04-24 Hitachi Ltd Segmented straight line function generator
US3821524A (en) * 1972-01-14 1974-06-28 Bosch Gmbh Robert Digital electronic approximative function tracing method and apparatus
US3831011A (en) * 1973-02-28 1974-08-20 Halliburton Co Method and apparatus for compensating a manifestation of fluid flow for temperature and specific gravity

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3345505A (en) * 1960-10-24 1967-10-03 Gen Precision Systems Inc Function generator
US3412240A (en) * 1963-02-21 1968-11-19 Gen Precision Systems Inc Linear interpolater
US3373273A (en) * 1964-04-17 1968-03-12 Beckman Instruments Inc Analog function generator including means for multivariable interpolation
US3480767A (en) * 1967-06-12 1969-11-25 Applied Dynamics Inc Digitally settable electronic function generator using two-sided interpolation functions
US3729625A (en) * 1970-06-05 1973-04-24 Hitachi Ltd Segmented straight line function generator
US3678258A (en) * 1970-09-29 1972-07-18 Electronic Associates Digitally controlled electronic function generator utilizing a breakpoint interpolation technique
US3821524A (en) * 1972-01-14 1974-06-28 Bosch Gmbh Robert Digital electronic approximative function tracing method and apparatus
US3831011A (en) * 1973-02-28 1974-08-20 Halliburton Co Method and apparatus for compensating a manifestation of fluid flow for temperature and specific gravity

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4160272A (en) * 1978-01-05 1979-07-03 Martin Marietta Corporation Digital voltage accumulator
US4205386A (en) * 1978-03-01 1980-05-27 The Valeron Corporation Electrocardiographic and blood pressure waveform simulator device
US4190896A (en) * 1978-09-05 1980-02-26 Bell Telephone Laboratories, Incorporated Circuits having substantially parabolic output versus linear input characteristics
US4318183A (en) * 1978-12-22 1982-03-02 Raytheon Company Multiple channel digital memory system
US4393740A (en) * 1979-03-23 1983-07-19 The Wurlitzer Company Programmable tone generator
US4326260A (en) * 1980-07-07 1982-04-20 Norlin Industries, Inc. Linear piecewise waveform generator for an electronic musical instrument
US4482975A (en) * 1982-03-29 1984-11-13 Motorola, Inc. Function generator
US4667298A (en) * 1983-12-08 1987-05-19 United States Of America As Represented By The Secretary Of The Army Method and apparatus for filtering high data rate signals
US4809203A (en) * 1986-08-25 1989-02-28 Ford Aerospace & Communications Corporation Hybrid analog-digital filter

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DE2539628A1 (de) 1976-03-18
GB1501877A (en) 1978-02-22

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